Elesclomol (also known as STA-4783), originally identified in a cell-based phenotypic screen for pro-apoptotic activity, is a novel small-molecule that potently induces apoptosis of cancer cells through the rapid generation of reactive oxygen species (ROS) and the induction of unmanageable levels of oxidative stress. Elesclomol exhibits antitumor activity against a broad spectrum of types of cancer cell in human tumour xenograft models due to its excessive ROS production and elevated levels of oxidative stress leading to the death of cancer cells. Elesclomol is currently being studied as novel cancer therapeutic, in which it has demonstrated the ability to prolong progression-free survival in study subjects. Elesclomol induces oxidative stress by provoking a buildup of reactive oxygen species within cancer cells. Elesclomol requires a redox-active metal ion to function; the Cu(II) complex is 34 times more potent than the Ni(II) complex and 1040-fold more potent than the Pt(II) complex. Elesclomol is an HSP-90 Inhibitor with pro-apoptotic and potential antineoplastic activities. Elesclomol induces oxidative stress and triggers mitochondrial-induced apoptosis in cancer cells. Elesclomol is being developed by Synta Pharmaceuticals and GlaxoSmithKline as a chemotherapy adjuvant and has received both fast track and orphan drug status from the U.S. Food and Drug Administration for the treatment of metastatic melanoma. Synta Pharmaceuticals announced on February 26, 2009, the suspension of all clinical trials involving Elesclomol due to safety concerns. In March 2010, Synta announced that the FDA had approved resuming clinical development of elesclomol, and that they expected to initiate one or more clinical trials for elesclomol in the second half of the year. In a small, randomized phase II study, elesclomol was shown to significantly increase progression-free survival in people with metastatic melanoma when given in addition to paclitaxel (Taxol).